In communication devices, duplexers functionally provide the ability to receive and transmit signals while utilizing the same antenna. In usual transmission operations of a communication system, audio signals, which are typically fed into a microphone, are converted to a modulated signal by a modulator that is then converted to a designated carrier frequency by an oscillator. Thereafter, the signal passes through an interstage filter, which selects only a signal having a desired transmission frequency, and is then amplified to the desired signal intensity by a power amplifier, the output of which is fed to an antenna duplexer. The antenna duplexer passes only the signals of the designated transmission frequency to the antenna, which transmits the signal as a radio signal into the air.
In receiving operations, a signal received by the antenna is transmitted to the antenna duplexer to select only a signal of a designated frequency. The selected signal is generally amplified by a low-noise amplifier and transmitted through a signal converter where only a desired characteristic or signal is selected by filters within the signal converter. The signal is down-converted to baseband and then manipulated as an audio signal. An antenna duplexer is usually positioned between the antenna and down-converter circuits and has such a function that the transmission signal and the reception signal are isolated to prevent interference between the two types of signals.
Electrically a duplexer is a device using distinctly tuned resonant circuits to isolate a transmitter from the receiver, allowing the transmitter and the receiver to operate on the same antenna at the same time without the transmitter adversely affecting the receiver. Duplexers use filters, such as various pass band filters and notches to accomplish isolation and continuity in signal transfer. In duplexer operation, filters must pass the desired signal while rejecting as much as possible of the undesired signals. For example, all of the transmitter's energy is not contained in just the desired frequency; transmitters characteristically generate a wide band noise for a considerable width around the center frequency. Therefore, a reject band [or notch] filter may be used to refine the signal within the device. Within the art, a combination of complex or simple filters may be used to obtain the desired performance of the communication device.
The antenna duplexer necessarily has at least a transmission filter and a reception filter, and in order to prevent interaction between the transmission filter and the reception filter, it also has a matching circuit, which is also referred to as a phase matching circuit or a line pattern for phase matching. While an antenna operates as an interface between circuits and space, which transfers power between space and the transmitter (Tx) or receiver (Rx), its impedance acts as the load for the Tx or the input impedance for the Rx. This impedance is determined by such factors as electrical properties or environmental properties (e.g. surrounding conducting or insulating objects), generally categorized as ohmic resistance and radiation resistance but is also partially manifested as reactance. As with all devices that transfer energy, an antenna correspondingly has efficiency associated with its operation, namely, the measurement of the dissipated power within the antenna due to ohmic resistance of the antenna conductor and other losses. Optimized impedance matching to the antenna maximizes the power transferred between space and circuits.
Within the design of communication devices, computer simulations, tedious manual computations, or Smith Charts may be utilized to perform impedance matching. Manual computations typically involve complex conjugate calculations and numerous equations. Computer simulations are typically dedicated to design functions and not impedance matching. Such simulations require designer familiarity with multiple data inputs and their associated correct formats, and understanding voluminous results data. Smith Charts, or simulations that incorporate Smith Charts, are not only used for finding matching networks component values or maximum power transfer but are also used with such design tasks as optimizing for the best noise figures, ensuring quality factor impact, and assessing stability analysis.
In addition to the generalization of duplexer complexities, recent development of the mobile phone has resulted in the expansion of diverse functionality in communication devices that further complicates duplexer design. For example, increased device functions such as dual mode (e.g., a combination of an analog mode and a digital mode, or a combination of digital modes, such as TDMA (time division multiple access) or CDMA (code division multiple access)), and a dual band (e.g., a combination of an 800 MHz band and a 1.9 GHz band, or a combination of a 900 MHz band and a 1.8 GHz band or a 1.5 GHz band) have been increasing the complexity of device architecture and circuitry. Increased implementation of frequency related functions affect antenna bandwidth. Antenna bandwidth is generally the range of frequencies over which the antenna can operate while some other characteristic remains in a given range. Therefore, increased frequency ranges increases demand for performance over a number of frequency channels, or a wide bandwidth antenna. Moreover, to support these multiple, diverse functions while maintaining proper isolation and reliable signal transfer between Tx and Rx operations, present communication devices use fixed, redundant circuitry, such as an increased quantity of switches and filters to compensate and broaden duplexer capabilities. Accordingly, such increased use and quantity of filters synergistically creates the need for optimizing filter performance.
Ubiquitous to the electronics field and universal to the communications field is the continuing demand for component reduction and high performance devices. Elimination of redundant components, functions, or circuitry is highly desired in communication electronics. Similarly desired is increased performance in communication devices without increasing device size, weight, or price. Within the field, these individual design factors [goals] are frequently pursued independently while balancing impacts to other factors. Common within the field is the optimization of one factor, such as device performance, while maintaining or sub-optimizing another factor, such as redundant components.
Although frequency ranges of the communication system often determine the type of technology used in device design (e.g., MEMS (Micro-Electro-Mechanical Systems)), prospective uses of the radio frequency spectrum are driving the need for higher performance devices with reduced circuitry/architecture. For example, the FCC sanctioned “cognitive radio” purports to use non-assigned spectrum based on the condition that there be no present, real-time use occurring. This projected use imports future designs and concepts that are time-based with an increased number of bands—further demanding higher performance and greater architecture.
Given the aforementioned duplexer issues, tunable duplexers provide a form of alternate solutions. Present tunable duplexer designs and techniques incorporate one of two approaches: (1) using multiple filters for increased demand in bandwidth on each side of circuitry, i.e., for the Tx side and one for the Rx side, or (2) incorporating the use of a circulator, a bulky three port device for directional management and isolation. However, these schemes have proven limitations in today's communications field. For example, the use of multiple filters frequently incorporated the use of switched filters and substantially increased the amount of circuitry needed to accomplish functionality. This design approach also makes for difficult or clumsy impedance matching and performance solutions with either multi-throw switches or cascaded lower throw switches, in addition to the multiple filters. This approach is in conflict with the goal of optimizing filter performance. For the second approach, circulators are big, heavy, and are typically narrow band components, which use magnets for appropriate biasing. Additionally, broader band applications or needs result in larger componentry (e.g., circulator matching, support circuitry, etc.). Also, isolation capabilities within circulators are limited. Therefore, if not properly aligned, circulators adversely effect the optimization of filters.
In general, obstacles encountered by present day duplexers include, but are not limited to, impedance matching, reliable and quality signal transfer, and complex or cumbersome filter designs to support increase functional demand and Tx-Rx isolation. Moreover, fixed filter designs are commonly used to sustain multiple bands. In the situations where tunable duplexers are used, present methods or designs are ineffective.
It is desirable, therefore, to provide a system and method that overcomes these and other disadvantages.